Extracorporeal blood treatment means taking the blood from a patient, treating the blood outside the patient, and returning the treated blood to the patient. Extracorporeal blood treatment is typically used to extract undesirable matter or molecules from the patient's blood, and/or to add beneficial matter or molecules to the blood. Extracorporeal blood treatment is used with patients incapable of effectively eliminating matter from their blood, for example in the case of a patient who is suffering from temporary or permanent kidney failure. These and other patients may undergo extracorporeal blood treatment to add to or to eliminate matter from their blood, to maintain an acid-base balance or to eliminate excess body fluids, for instance.
Extracorporeal blood treatment is typically performed by sampling the patient's blood in a continuous flow, by introducing the blood into a primary chamber of a filter that is defined, at least in part, by a semi-permeable membrane. The semi-permeable membrane may selectively allow the unwanted matter contained in the blood pass through the membrane, from the primary chamber to the secondary chamber, and may selectively allow the beneficial matter contained in the liquid going into the secondary chamber pass through the membrane to the blood going into the primary chamber, according to the type of treatment.
A number of extracorporeal blood treatments may be performed by the same machine. In ultrafiltration (UF) treatment, the unwanted matter is eliminated from the blood by convection through the membrane in the secondary chamber.
In hemofiltration (HF) treatment, the blood runs through a chamber that is defined, at least in part, by a semi-permeable membrane as in UF, and the beneficial matter is added to the blood, typically by the introduction of a fluid into the blood, either before, or after its passage through the filter and before it is returned to the patient.
In hemodialysis (HD) treatment, a secondary fluid containing the beneficial matter is introduced into the filter's secondary chamber. The blood's unwanted matter crosses the semi-permeable membrane by diffusion and penetrates into the secondary fluid, and the beneficial matter of the secondary fluid can cross the membrane and penetrate into the blood.
In hemodiafiltration (HDF) treatment, the blood and the secondary fluid exchange their matter as in HD, and further, matter is added to the blood, typically by introducing a fluid into the treated blood before it is returned to the patient as in HF; unwanted matters are eliminated from the blood by convection and diffusion.
In those treatments using a secondary fluid, the secondary fluid goes through the filter's secondary chamber and receives the blood's unwanted matter by diffusion and/or convection through the membrane. This liquid is then extracted from the filter: it is commonly called effluent, and is sent to a drain or to a receptacle then intended to be discharged into a drain.
In the extracorporeal treatments that use a secondary fluid, the secondary fluid may be supplied in a sterile single-use bag as illustrated in FIG. 1. For purposes of this discussion, the secondary fluid may be dialysate contained in a dialysate bag 11. The dialysate bag 11 delivers dialysate to the secondary chamber 4 through an exit line 9. This bag 11 is combined with a gravimetric scale 21 linked to a control unit 41. Thus, weight signals are transmitted to the control unit 41 that is capable of monitoring the weight changes of the bag 11 and to control a pump 31 acting on the exit line 9 (i.e., the line delivering dialysate from the bag 11 to the secondary chamber 4).
Regardless of whether the control of dialysate delivery is accomplished gravimetrically or volumetrically, a single-use dialysate bag 11 is often emptied well before the end of the session. This phenomenon is all the more pronounced during an intensive treatment. Indeed, one wishes both to exchange a large quantity of liquid in HF or HDF therapy, and to perform long-term treatments.
As soon as the bag 11 reaches a set level (or at another time as selected by a user), the pump acting on the exit line 9 (and other pumps as needed) may be temporarily stopped, while the blood may continue to circulate extracorporeally in the filter's primary chamber 3. Once the pump 31 is stopped, the user has to disconnect and unhook the empty dialysate bag 11. Then the user attaches and connects a new full single-use bag 11 to the treatment apparatus and restarts the pump(s) to return to the extracorporeal treatment with fluid circulation through the two chambers (3, 4) of the filter 2.
This bag replacement operation has several potential disadvantages. The operation is performed by health care personnel who have to monitor several patients at the same time (a waiting time before action by the personnel typically increases therapy down time and may require additional treatment time or result in decreased treatment efficiency), and the regular changing of the dialysate bag during a session adds an economic cost to the treatment.
Although described herein in connection with the delivery of dialysate, it should be understood that similar issues may be encountered in blood treatment apparatus in which infusion fluids are delivered into the blood (whether before or after filter or before the blood pump). For purposes of the discussions herein, any such fluids will be referred to as “treatment solutions” which may include, e.g., dialysate; a replacement fluid of a convective replacement therapy of the renal function; plasma, albumin or colloid solutions that may be used in Therapeutic Plasma Exchange (TPE); or any other known type of medical fluid for replacement therapy.